The user equipment (UE) can employ multiple receiver branches irrespective of the access technology or radio interface design. Typically there can be two receiver branches at the UE. This is commonly termed as receiver diversity. There are several benefits such as cell coverage is extended, efficient use of transmitted power at the base station etc. In Additive White Gaussian Noise (AWGN) two receiver branches can boost the system capacity by 3 dB. However, multiple branches at the UE can also drain more power, thereby reducing the UE talk or usage time in some scenarios. Therefore, in scenarios where receiver diversity does not lead to any system gain, it is advantageous from UE battery perspective to switch off its additional receiver branches.
The receiver diversity comprising of two receiver branches at the UE is being used in WCDMA. In the standard, receiver diversity is a UE capability and it is ensured by specifying UE receiver requirements and is called enhanced performance requirements type 1.
The receiver diversity (or type 1 requirements) is specified for number of scenarios in terms of downlink physical channels. The scenarios employing the receiver diversity include HSDPA, MBMS, DCH and Enhanced Uplink (EUL) downlink channels. The physical channels that currently use receiver diversity are: HS-PDSCH and HS-SCCH for HSDPA scenario, DPCH and DPCCH for DCH scenario, MTCH for MBMS scenario and E-RGCH, E-HICH and E-AGCH for EUL scenario.
In E-UTRAN, receiver diversity at the UE is likely to be employed as the minimum requirements or a mandatory feature. Thus an E-UTRAN UE will use at least two receiver branches to receive all channels in all scenarios.
As mentioned above one implication of receiver diversity is increase in power consumption in some scenarios but not all. In such scenarios, where UE power consumption increases and network does not sufficiently benefit from having receiver diversity active all the time, it is advantageous from UE perspective to switch off one of its receiver branches if radio conditions are favorable. On the other hand the UE should switch on both receiver branches when radio conditions deteriorate. This switching on and off of receiver diversity in response to the radio conditions is called dynamic reconfiguration of UE enhanced receiver in 3GPP terminology.
In principle, dynamic reconfiguration concept can be utilized by the UE in all scenarios. However, in some scenarios there is an advantage from the network perspective that UE keeps its receiver diversity on all the time during a session. For instance in HSDPA scenario the channel dependent scheduling makes use of favorable radio conditions to increase user throughput. With the introduction of receiver diversity at the UE, the channel dependent scheduling in good radio conditions will further improve the user throughput. In addition high data rate transmission during a scheduling turn would require UE with receiver diversity on all the time, to be scheduled less often as compared to the one with single branch. Therefore, the average UE power consumption may not significantly increase in HSDPA scenario when receiver diversity is active consistently.
In 3GPP, point to multipoint MBMS scenario has been identified, where the dynamic reconfiguration of enhanced receiver in good radio conditions does not adversely impact the system performance. This is due to the fact that point to multipoint MBMS delivery is carried out by fixed transmission power level. This means that, when the UE moves close to the base station, or when it enters in good radio conditions, the UE can switch off its enhanced receiver (i.e. one of its branches), while still maintaining an adequate reception quality of the desired MBMS service.
From a network perspective, the desired quality of service should be fulfilled irrespective of whether UE receiver diversity is switched on or off. Therefore network is to signal the quality target in terms of BLER or SDU error rate to the UE even in point to multipoint MBMS scenario. This will eventually be used by the receiver reconfiguration algorithm at the UE. The exact algorithm is UE implementation dependent allowing the UE to autonomously switch on or off its receiver diversity.
In order to understand the switching algorithm, the following variables can be considered:                Measured quality: QM         Adjusted target quality: QT         Measured BLER: BLERM         
The measured quality QM is measured by the UE based on some known signals such as CPICH in WCDMA. Some examples of measured quality are CPICH RSCP, CPICH Ec/No, SINR, etc. The exact quantity chosen by the UE is implementation dependent.
The adjusted target quality QT is adjusted by the UE autonomously in accordance with the measured BLERM and its comparison with the target BLERT. The exact derivation and adjustment of the QT is thus implementation dependent. But for the sake of clarity the interpretation QT in this description is that it is increased by certain amount when measured BLER (BLERM) is lower than the target BLER (BLERT), otherwise it is decreased by certain amount.
The dynamic reconfiguration will work as follows:
IF QM>QT                 UE switches to single receiver branch        
ELSE (i.e. QM≦QT)                UE switches to dual receiver branches        
The UE capabilities for MBMS reception are specified in for example 3GPP TS 25.306, “UE Radio Access capabilities”. First of all more than one MBMS traffic channel (MTCH) that carries MBMS service can be mapped on to one physical channel (S-CCPCH) with a certain spreading factor. Secondly, a UE can receive more than one MTCH (i.e. more than one point to multipoint MBMS service at a time). The dynamic receiver reconfiguration should not degrade the received quality of any of all the services received by user.
In the current system, the underlying assumption is that user at a time is receiving one point to multipoint MBMS service, which is mapped onto one MTCH channel. Therefore the decision of the dynamic receiver reconfiguration is based on the measured quality of one particular service. In that case the switching principle stated previously is sufficient to ensure that the desired quality target is maintained. Reception of one service at a time is usual case.
However, in practice a user may intend to receive simultaneously more than one service, for example watching a football match and scanning weather forecast etc. In that case, the user will receive more than one MTCH, which may be multiplexed onto the same physical channel (i.e. S-CCPCH). Furthermore, the quality of service requirements of different services may be different. In addition, the physical channel configuration, by which we mean modulation, coding, rate matching etc., may significantly differ on different types of channels. However the algorithm described previously does not describe how the UE will dynamically reconfigure its enhanced receiver when it is actively receiving multiple services at a time.